Re: low em wave shield
From: Gregory L. Hansen (glhansen_at_steel.ucs.indiana.edu)
Date: 09/03/04
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Date: Fri, 3 Sep 2004 01:06:18 +0000 (UTC)
In article <3ba4d769.0409021233.59c34f98@posting.google.com>,
Paul <paulw@mmail.ath.cx> wrote:
>Hi
>
>Can someone give suggestion on how to block low frequency em wave?
>Specifically, low frequency em wave between 0-40 Hz (frequencies that
>can effect brain.) Thanks. I thinking about making a helmet.
Ferromagnetic materials, higher permeability is better. You could use
iron, but that's not great. The standard material is mu-metal, a
nickel-iron alloy that's pretty pricey. Going to higher performance
brings you to Metglas, ribbons of amorphous metal alloys.
Even a skull cap will provide some shielding, but any holes will let field
leak in. Building a chimney around the hole will improve the shielding.
Several small holes are better than a big hole. Think of a knight's
helmet, with eye slits in the visor.
More than that, shielding is improved by using several thin layers with
proper spacing between them. Think of the sort of knight's helmet that
might have been worn by space warriors in a 1950's science fiction flick.
A little less bulky and more fashionable might be a series of solenoids
built into your headwear, with magnetometers that sense the field
strength, and an active control system that adjusts currents in the
solenoids to cancel the field.
-- "Let us learn to dream, gentlemen, then perhaps we shall find the truth... But let us beware of publishing our dreams before they have been put to the proof by the waking understanding." -- Friedrich August Kekulé
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